Industries have struggled to provide systems that allow their plants and processes to meet federal and state regulations regarding clean air emissions. One of the successful techniques which has allowed industries to become compliant has been the use of catalytic converters to process gaseous streams prior to release to the environment. One such process is known as selective catalytic reduction, or SCR, which serves as one possible option for lowering or even substantially lowering the levels of nitrogen oxides formed during the combustion of fossil fuels in combustion plants. Particularly, catalysts that are used in so-called deNOx or dedioxin installations are used for reducing and breaking down nitrogen oxides.
In the SCR process, the nitrogen oxides are converted into nitrogen and water using ammonia or substances which form ammonia under the system conditions as a reducing agent and catalysts in the catalytic converter. Typical catalysts for use in these processes comprise a base material, for example titanium dioxide, TiO2, in which active metal compounds, for example, V2O3 and/or WO3, are homogeneously distributed. Because the catalytic reactions proceed on the surface of the catalyst, a large specific surface area is typically provided through the use of correspondingly porous materials for the reaction, for example, in a honeycomb structure.
However, due to the accumulation of alkali metals, alkaline earth metals, or other particulates, which are contained in fly ash, the reaction at active centers on the catalyst becomes partially, and in some cases substantially, impeded. Therefore, the nature of the composition of the compounds which may be deposited on the catalyst is dependent on the composition of the fly ash. Generally, the removal of fly ash from catalytic converters is well known in the art.
In addition to typical fly ash, harder, larger ash particulate, referred to in the industry as popcorn ash, has become a problem in catalytic converters as a combustion by-product of certain fuels used in North American fossil fuel power plants. The lifespan of new catalysts becomes significantly reduced because of the build up of popcorn ash inside the channels of catalytic converters. Popcorn ash consists of large particles of fused ash that can become very hard, and have irregular shapes. Some popcorn ash can have orientations which are narrow enough to fit into the channels of the catalytic converter, while others are too large to fit. When popcorn ash enters the catalytic converter along certain orientations, it becomes lodged in the catalytic converter. The lodging of the popcorn ash can cause normal fly ash to fill the rest of the channel of the catalytic converter, thereby essentially blocking the catalyst channel, such that few or no reactive catalyst sites are available to perform the intended reduction reactions on the nitrogen oxides.
Conventional processes for fly ash removal are typically not effective for substantially complete removal of popcorn ash. It has also been determined that forcing the popcorn ash through the catalytic converter will only further lodge the popcorn ash, and therefore, further impede the catalytic converter. Moreover, attempts to remove popcorn ash using wet/dry vacuums results in collapse of channel structure in the catalytic converter. Accordingly, a need exists for techniques to effectively remove popcorn ash from catalytic converters.